1. Field of the Invention
The present invention relates to an elastic wave resonator including an IDT electrode that is mounted on a piezoelectric substrate, and to an elastic wave filter and a duplexer each including such an elastic wave resonator.
2. Description of the Related Art
Elastic wave resonators have been widely used as resonators for band filters to be used in cellular phones and the like. For example, in Japanese Unexamined Patent Application Publication No. 2-127809, an elastic wave resonator including a piezoelectric substrate and an interdigital transducer (IDT) electrode mounted on the piezoelectric substrate is disclosed. Japanese Unexamined Patent Application Publication No. 2-127809 describes a structure where electrode fingers having different widths are arranged at intervals within the IDT electrode.
However, as in the elastic wave resonator of the Japanese Unexamined Patent Application Publication No. 2-127809, even in cases where electrode fingers having different widths are arranged at intervals within the IDT electrode, depending on values of the different widths of the electrode fingers, non-linear signals are not sufficiently reduced in some cases. Therefore, when the elastic wave resonator of the Japanese Unexamined Patent Application Publication No. 2-127809 is used in a transmission filter of a duplexer, in some cases, noise in a reception band of the duplexer increases, and reception sensitivity decreases.